This invention relates to self-closing valves for packaging containers, that is to say, valves which open in response to an elevated pressure of the liquid product in a packaging container, and which close again automatically and in a self-sealing manner when the pressure has subsequently been reduced to below ambient pressure.
Self-closing valves are well known in the patent literature, and examples of them are disclosed in published patent specifications EP 0545678, EP 0395380, FR 996998, U.S. Pat. No. 2,758,755, U.S. Pat. No. 2,175,052 and WO 97/05055 amongst many others. Self-closing valves have been proposed for use with a wide variety of liquid foods e.g. ketchups, and household products e.g. washing-up liquids.
The requirements of a self-closing valve to dispense product in a controlled manner when required and to automatically reseal after dispensing tend to conflict with one another insofar as the configuration of the valve is concerned. Amongst the other requirements which may impose further restraints on the valve design are the need for the valve head to adopt an advanced position for the dispensing operation, and for the valve to be capable of being readily sealed, against inadvertent operation or dribbling, by a travel head with which it is engaged up to the point of use. In addition, for cleanliness of operation it may be preferred for the valve head at all times to stand proud of the closure in which the valve is mounted.
A further desirable characteristic of a self-closing valve is that it is capable of venting the container headspace in response to small negative pressures which are generated there after dispensing. This is of particular concern where the containers are plastics squeeze bottles which for economy have a reduced wall thickness, e.g. 0.4 mm, and a correspondingly reduced ability to resile when they are allowed to relax. Without the ability of the valve to vent, such a container may be subject to unsightly inward panelling and crumpling of its body wall. Satisfactory venting and reclosure of a self-closing valve in response to negative pressures of 1 kPa or less is therefore desirable.
In attempting to meet the various requirements imposed upon them known self-closing valves have been made from a substance having advanced physical properties, in particular of flexibility and resilience. Liquid silicon such as is marketed by Bayer under the trade name Silopren has been particularly preferred for this purpose, although thermoplastic elastomers have also been contemplated.
These materials are expensive in comparison with the thermoplastic resin materials usually used for packaging, and for cost savings it is therefore desirable, as a further objective, to minimise the material weight of the valve.